The field of this invention relates to downhole screens, which can be expanded into contact with the formation.
Downhole screens are used in a variety of different applications. As part of a common procedure called gravel packing, the screens are deposited adjacent the producing formation and the surrounding annular space is filled with sand known as gravel. Various fabrication techniques have been developed for manufacturing such screens and a typical example is illustrated in U.S. Pat. No. 5,611,399.
More recently it has been determined that it is desirable to reduce the size of the annular space between the screen and the formation. Reduction of the volume of the annular space around the screen discourages fluid flow along the screen, which, in turn, lessens the production of sand. In order to be able to produce the reservoir longer, it has been desirable to insert screens in well bores or laterals and thereafter expand them. A good example of the expansion techniques for a downhole screen is shown in U.S. Pat. No. 6,012,522. In this patent, overlapping segments of screen are placed on a base pipe, which is ultimately expanded from within when placed in position in the well bore or a lateral. The shortcoming of this technique is that portions of the filtering material must be moved relative to each other which subjects them to tearing which in turn can result in a failure of the expanded screen assembly to control the production of sand. Another shortcoming of such designs is the limited capacity to withstand collapse.
Other patents relating to pipe expansions are: U.S. Pat. Nos. 5,901,789 and 5,366,012.
The main objective of the present invention is to allow easy installation of the screen to the desired location followed by expansion to reduce the volume of the annular space around the screen. Yet another object of the invention is to expand the screen against the formation to entirely eliminate the annular space around it. Yet another objective of the present invention is to allow the use of the structure of the screen downhole even without expansion. Another objective of the present invention is to decrease the amount of stress on the filtration member when expanded. Yet another objective of the present invention is to provide a significantly stronger structure for the finished product, which even after expansion presents a greater resistance to collapse. Another object of the invention is to provide, as much as possible, uniformity in the opening size of the filtration layer after the assembly is expanded. Another objective is to provide sufficient strength in the assembly, after expansion to allow it to better resist differential pressures. Still another objective is to reduce the effort required for expansion and to stage the overall expansion in discrete steps. These and other advantages of the present invention will be appreciated by those skilled in the art from a review of the description of the preferred embodiment, which appears below.
A downhole completion method and an expandable filtration apparatus are disclosed. The filter assembly comprises a plurality of layers beginning with a coated perforated base pipe. The coating reduces the force required for expansion. A drainage layer overlays the base pipe with the filtration layer above it. The drainage layer improves flow through the filtration layer and protects it from burrs in the base pipe. A filtration enhancement layer fits over the filtration layer and an outer shroud protects the assembly during run in. The assembly can be used as made or expanded downhole in one or a series of expansions.